Cartridge fuses



Matchs, 1963 F. J; KOZACKA 3,080,463

CARTRIDGE FUSES Filed Dec. 23, 1960 2 Sheets-Sheet 1 Invezzoa.-

Jlozaa,

L 'y AWM Wt-01422439 March 5, 1963 F. J. KozAcKA 3,080,463

CARTRIDGE FUSES Filed Dec. 25, 1960 2 sneetsfsneet 2 Iaavenww.- E4 ,1w J.' Kozacb,

y www@ United States Patent C i 3,086,463 CARTRBGE FUSES Frederick J. Kozacka, South Hampton, NH., assigner to The Chase-Shawmut Company, Newburyport, Mass. Filed Dec. 23, 1960, Ser. No. 78,12l Claims. (Cl. Ztltl--lti This invention relates to electric cartridge fuses, and more particularly to cartridge fuses of the blade contact type.

Cartridge fuses required to have a relatively high interrupting capacity, or required to have a current limiting action, include fuse links of a metal having a relatively high conductivity and a relatively small fusing energy. Silver and copper comply best with these requirements. Fuse links made of such metals are provided with points of restricted cross-sections, or necks, which determine the location where circuit interrupting arcs are kindled along the links when the fuse blows on occurrence of shortcircuit currents. The geometry of these points ot reduced cross-section, or necks, further determines the ft2-dt required to cause blowing of the fuse on occurrence of short-circuit currents. Fuses which are required to blow fast on occurrence of short-circuit currents require points of restricted cross-sections, or necks, which have but a small fraction of the normal cross-section of the fuse link. Such points of reduced cross-section, or necks, tend to impair the mechanical integrity of fuse links of the aforementioned character, i.e. there is an imminent danger of breakage of links formed by ribbons of silver o1' copper if such ribbons have very narrow necks to make the fuses relatively fast.

It is, therefore, one object of this invention to provide fast blade type cartridge fuses having link structures whose dimensional stability is sufficiently high to substantially exclude the danger of breakage during handling, or while the product is in transit.

Another object of the invention is to provide blade Contact type cartridge fuses comprising ribbon type fuse links of silver or copper directly conductively connected to the blade type contacts, which fuses include means 4for protecting the points or" reduced cross-section, or necks, of the links from bending stresses that normally occur when the spacing between the blade type contacts is accidently slightly reduced during handling of the product, or while the same is in transit.

Another object of the invention is to provide blade contact type fuses comprising an insulating spacer between lthe blade contacts adapted to evolve an arc-quenching blast of gas when the fuses blow.

The foregoing and other general and special objects of the invention and advantages thereof will more clearly appear from the ensuing particular description of the invention, as illustrated in the accompanying drawings, wherein FIG. l is a longitudinal section along 1-1 of FIG. 2 showing a tirst embodiment of the invention;

FIG. 2 is a section along 2--2 of FIG. l;

f FIG. 3 is a section similar to that of FIG. 1 showing a modification of the structure ot FIGS. l and 2;

FIG. 4 is an exploded isometric view of the constituent parts ot the structure of FIGS. l and 2;

FIG. 5 shows a modified detail of the structure of FIGS. l and 2; and

FIG. 6 is a section along 6 6 of FIG. 5.,

Referring now to the drawings, and more particularly to FIGS. 1, 2 and 4 thereof, numeral 1 has been applied to indicate a casing of an insulating material, e.g. a synthetic-resin-berglass cloth laminate. The laminate may be, for instance, a melamine-ber-glass-cloth laminate. A pair of-aligned blade contacts 2 projects axially out- "ice wardly from the axially outer ends of casingr 1. Blade contacts 2 have axially inner edges 2a arranged inside of casing l and defining a gap G therebetween. Casing 1 is filled with a pulverulent arc-quenching iiller 3 as, for instance, quartz sand which has been carefully purified. Reference numeral 4 has been applied to indicate a strip of insulating material aligned with blade contacts 2 and arranged in the gap G formed between blade contacts 2. Strip 4 may also be formed by a synthetic-resin-fiber-glass cloth laminate. The axially outer edges 4a of strip 4 are arranged in abutting relation with the axially inner edges of blade contacts 2. Thus strip 4 forms a spacer between the edges 2a of blade contacts 2. Ribbon fuse link 5 is arranged substantially parallel to strip 4. It consists of a metal having a relatively high conductivity and a relatively small fusing energy, preferably silver, or possibly copper. Link 5 has axially outer ends 5a extending axially outwardly beyond the axially outer edges 4a of strip 4. Each axially outer end 5a of link 5 is conductively connected to one of blade contacts 2 as, for instance, by brazing or by a mechanical joint (not shown). Fastener means 6 project transversely through strip 4 and fuse link 5 securing strip ito link S. Fastener means 6 are preterably staples as generally used for stapling sheets of paper or cardboard. The stables 6 are of steel but arranged suiiiciently far from the arcing zone of the fuse to preclude vaporization thereof by arcing during the interrupting process.

Fuse link 5 is provided with a plurality of serially related points of reduced cross-section. Each point of reduced cross-section is formed by a transverse line 5b of circular perforations. The perforations in each line 5b and of all three lines 5b are identical. At each line Sb of perforations the cross-section of the link decreases progressively from left to right to a point of minimal cross-section, and then increases progressively from left to right. Numeral 7 has been applied to indicate a linkdestroying overlay of a relatively low fusing point metal, eg. tin, extending from a point of link remote from the points of minimal cross-section to one of the points of minimal cross-section but not beyond said one of said points of minimal cross-section, In other words, overlay 7 extends from a point of link 5 to the lett of the median plane of the link which is a point of minimal crosssection-to, but not beyond, the median plane of the link. Hence all three serially related points of reduced or minimal cross-section formed by lines 5b have the same fusing ft2-dt the latter being a constant well known in the fuse art which does not need to be explained in this context. Overlay '7 abstracts heat from the median plane of the fuse link where it is generated and thus delays blowing of the fuse at relatively small overloads. On occurrence of short-circuit currents heat generation occurs at such a rapid rate that overlay 7 cannot abstract heat from the median plane of the fuse link where it is generated and, therefore, all three points of reduced crosssection or minimal cross-section fuse substantially simultaneously on occurrence of short-circuit currents. The point of reduced cross-section situated in the median plane of the fuse link has the dual function to form a break on the occurrence of small protracted overloads as Well as to form a break on occurrence of short-circuit currents. In the latter case two additional breaks are formed at the two transverse lines 5b of circular periorations adjacent the axially outer ends of the fuse link 5. The use of overlays of 'low fusing point metals such as tin or alloys of tin on fuse links of silver and copper is well known as a means oi effecting link destruction by a metallurgical reaction between the overlay metal and the base metal, and the nature of this reaction does, therefore, not need to be described in detail in this context. Sutiice it to say that as long as the fuse does not blow no point of the fuse i `project from `the axially outer ends of casing 1.

link can reach a higher temperature than the relatively low fusing temperature of the overlay metal. This is important because it makes it possible to make strip 4 of a material which is not particularly heat resistant as, for instance, a rnelamine-glass-cloth laminate. if more heat resistance is required one may resort to silicone-glasscloth laminates. Duringnormal operation, i.e. as long as the fuse` does not blow, no point of the structure can ever assume an operating `temperature exceeding the fusing point of overlay 7. n

As shown in FiGS. 1, 2 and 4, casing l is closed by a pair of discs ii of asbestos or the like having rectangular perforations 7u for the passage of blade contacts 2. Casing l is closed by a pair of caps or ferrules 9 mounted on the ends thereof and held in position by pins 1li projecting through blade contacts 2 and casing l. The nature of this pin mount is more fully described in U.S. Patent 2,939,935 to F. I. Kozacka, Fuse Structures, issued June 7, 1960.

FlG. 3 illustrates a modification of the structure of MGS. l, 2 and 4 which admits high spot temperatures on link` These temperatures are suthciently high to impair the insulating support or strip 4 if the hot spots of link '5i were in physical engagement with strip 4. According to HG. 3 link 5 has a plurality of transverse convex portions 5c spaced from strip 4' each defining one of a plurality of serially related points of reduced crosssection. Each of said plurality of points of reduced crosssection is formed by a transverse line of circular perforations having the centers thereof in the peaks of said convex portions. The spacing between the hottest points of the fuse link structure and strip 4 is suicient to prevent thermalA damage to the latter even if the highest spot temperatures on link :3" are quite high.

in other respects the structure of FIG. 3 is substantially the same as that shown in FIGS. l, 2 and 4. The tubular casing l of insulating material is tilled with the pulverulent arc-quenching hller 3l and the two blade contacts 2 The axially inner edges 2a of blade contacts 2' abut against the axially outer edges of insulating strip 4'. Casing 1 is closed by washers 7 and ferrules 9', pins 10 projecting through parts 2', l and 9.

ln the modiiication of the invention shown in` FIGS. 5 and 6 the insulating strip 4" is supposed to be arranged in Ythe same way as the insulating strips 4 and 4' in FIGS.

l-4. Fuse link 5" has one single point of reduced crosssection or neck 5c. Strip 4 is provided with a circular opening ab" giving access of pulverulent arc-quenching filler 3 to neck 5c".

It will be apparent that in all embodiments of the invention the spacing 'strip 4, 4', 4 of insulating material andthe ribbon fuse link 5, 5', 5 form a sub-assembly making it possible to readily handle the yfragile link during the process of manufacturing the fuse without any danger of bending, or otherwise damaging, the link at the narrow t neck portion or portions thereof.

ing su-bmersed in said filler and having axially outer ends extending axially outwardly beyond said axially outer edges of said strip each overlapping and conductively connected to the outer surface of one of said pair of blade contacts; and fastener means projecting transversely through'said strip and said link securing said strip to said link.

2. An electric cartridge fuse as specified in claim l comprising a link having points of reduced cross-section and aperture means in said strip adapted to give to said iiller access to said points of reduced cross-section.

3. An electric cartridge fuse comprising in combination a tubular casing of insulating material; a pulverulent arcquenching filler inside of said casing; a pair of aligned blade contacts projecting axially outwardly from the axially outer ends of said casing and having axially inner edges arranged inside of said casing defining a gap therebetween;

a strip of organic insulating material evolving a gas under the heat of an arc aligned with said pair of blade contacts, arranged in said gap, and having axially outer edges in abutting relation with said axially inner edges of said pair of blade contacts; a ribbon fuse link of a metal having a relatively highconductivity and a relatively small fusing energy submersed in said filler, said link being arranged substantially in the plane defined by said strip and having a plurality of serially related identical points of minimal cross-section and axially outer ends extending axially outwardly beyond said axially outer edges of said strip each conductively connected to one of said pair of blade contacts; a link-destroying overlay of a metal having a relatively low fusing point on said link extending from a point thereof remote from said plurality of points ofY minimal cross-section to one of said plurality of points of minimal cross-section but not beyond said one of said plurality ofA points of minimal cross-section whereby said plurality of points of minimal cross-section are caused to have substantially the same fusing ft2-dt in spite of the presence of said overlay; and fastener means projecting transversely through said strip and said link securing said strip to said link.

` 4. An electric cartridge fuse comprising in combination a tubular casing of insulatingrmaterial; a pulverulent arcquenching liller inside of said casing; a pair of aligned blade contacts projecting axially outwardly from the axially outer ends of said casing and .having axially inner edges arranged inside of said casing defining agap therebetween; a strip of insulating material aligned with said pair of blade contacts, arranged in said gap, and having axially outer edges in abutting relation with said axially inner edges of saidpair of blade contacts; a ribbon fuse link of a metal having a relatively high conductivity and a relatively small fusing energy submersed inY said filter, said link being arranged substantially parallel to said strip, said i' link having a plurality transverse convex portions spaced It will be understood that I have illustrated and det scribed herein preferred embodiments of the invention, and that various alterations may be made in the details thereof without departing from the spirit of the invention as defined in the appended claims.V

I claim: Y

l. An electric cartridge fuse comprising in combination a tubular casing of insulatingmaterial; a pulverulent arcquenching iiller inside vof said casing; a pair of terminal caps closing the ends of `said casing; a pair of aligned blade contacts projecting transversely across said pair of caps and having axially inner edgesarranged inside said casing dening a gap therebetweenga strip of insulating material aligned with said pair of blade contacts, arranged in said gap, and having axially outer edges in abutting relation with said axially inner edges of said pair of blade contacts; a ribbon fuse link of a metal having a relatively l high conductivity and a relatively small fusing energy arranged'substantially parallel to said strip, said link befrom said strip each Ydeiining one of a plurality of serially related points of reduced cross-section, said link further having axially outer ends extending axially outwardly beyond said axially outer edges of said strip each being conductively connected to one of said pair of blade contacts; and fastener means projecting transversely through said strip and said link securing said strip to said link.

l 5.. An electric cartridge fuse as specified inY claim 4 wherein each of said plurality of points of Vreduced crosssection is formed by a transverse line of circular perforations having the centers thereof in the peaksrof said convex portions.

References Cited in the file of this patent UNITED STATES PATENTS 1,907,739 Cunt May 9,l 1933 2,665,348 Kozacka QV.'. p Jan. 5,V 1954 2,681,399 fDetchk ,June 15, 1954 FORETGNPATENTS Y Y v 829,845 France VY. Apr.V 25, `193s 

1. AN ELECTRIC CARTRIDGE FUSE COMPRISING IN COMBINATION A TUBULAR CASING OF INSULATING MATERIAL; A PULVERULENT ARCQUENCHING FILLER INSIDE OF SAID CASING; A PAIR OF TERMINAL CAPS CLOSING THE ENDS OF SAID CASING; A PAIR OF ALIGNED BLADE CONTACTS PROJECTING TRANSVERSELY ACROSS SAID PAIR OF CAPS AND HAVING AXIALLY INNER EDGES ARRANGED INSIDE SAID CASING DEFINING A GAP THEREBETWEEN; A STRIP OF INSULATING MATERIAL ALIGNED WITH SAID PAIR OF BLADE CONTACTS, ARRANGED IN SAID GAP, AND HAVING AXIALLY OUTER EDGES IN ABUTTING RELATION WITH SAID AXIALLY INNER EDGES OF SAID PAIR OF BLADE CONTACTS; A RIBBON FUSE LINK OF A METAL HAVING A RELATIVELY HIGH CONDUCTIVITY AND A RELATIVELY SMALL FUSING ENERGY ARRANGED SUBSTANTIALLY PARALLEL TO SAID STRIP, SAID LINK BEING SUBMERSED IN SAID FILLER AND HAVING AXIALLY OUTER ENDS EXTENDING AXIALLY OUTWARDLY BEYOND SAID AXIALLY OUTER EDGES OF SAID STRIP EACH OVERLAPPING AND CONDUCTIVELY CONNECTED TO THE OUTER SURFACE OF ONE OF SAID PAIR OF BLADE CONTACTS; AND FASTENER MEANS PROJECTING TRANSVERSELY THROUGH SAID STRIP AND SAID LINK SECURING SAID STRIP TO SAID LINK. 